If this is to be a fair test I will have to control all of these variables. I will do this by keeping the temperature at 20 C and I will use the same thickness of magnesium ribbon. I will also keep the ph level the same by not adding any acid or alkalise to the solution.
To make this experiment safe I will wear goggles. Also if I happen to spill any acid or and other substance I will wipe it up straight away.
The independent variable I have chosen is the concentration. I will get different concentrations by using different ratios of acid to water. Before I did this test I did some pilot tests to see what would be suitable amounts of acid and magnesium. Here are my ratios of acid to water.
I am doing this experiment in two different ways firstly I will time how long it takes for a 1cm long strip of magnesium to disappear in the above concentrations. Secondly I will time how long it takes for 5cm of magnesium ribbon to produce 30cm of hydrogen. I will do each experiment twice so I will have more reliable data. Therefore I will have 4 results for each concentration, which should show clear trends.
Method
I carried out my first experiment by getting 25ml of acid I then put this into a beaker. Next I collected 1cm of magnesium ribbon and a stop clock. I dropped the magnesium in and timed how long it took for the magnesium to disappear. I then did the same for each of the other concentrations.
For the second experiment I gathered a side armed flask, a bung, a piece of rubber tubing, and a gas syringe. I fitted these together by attaching the tubing to the side armed flask and the gas syringe. I then collected by acid and 5cm of magnesium, I then put both the acid and magnesium into the side armed flask and put the bung on tightly so no gas leaked out. I timed this experiment and again did the same for each concentration. Conical flask
Gas syringe
Diagram
Rubber tubing
Magnesium
Acid
Hydrogen
Beaker
Magnesium
Acid
Results
Graph showing the rate at which, a 1cm piece of magnesium ribbon disappears in different concentrations of acid.
Graph showing the rate at which, 5cm of Magnesium produces 30ml of gas in different concentrations of acid.
Analysis
These results show that the higher the concentration of the acid, the quicker the rate of reaction will occur. My graph for producing 30ml of gas has a smooth curve going through all of the points. This clearly shows that as the concentration of the acid goes up so does the rate of reaction. However my graph, which shows the rate of reaction for the magnesium to disappear, is not quite so clear, as two points are not on my line of best fit. This maybe because it is difficult to judge when a piece of magnesium has actually disappeared. Or we may have been inaccurate in measuring out the different concentrations.
My prediction was correct as you can see from the results. This is because of the collusion theory, which I have mentioned in my planning. It basically states that the rate of reaction will increase if the concentration of the acid increases. This is because at a higher concentrations of acid the magnesium will collide with more acid molecules than if it was in the lower concentration of acid, this means there will be more successful collisions resulting in the rate of reaction going up. Most of my results support my prediction and even the two slightly odd results still show the same general pattern.
Evaluation
I think this was a successful experiment as my results show clear trends, which I have supported with scientific backup. My prediction was correct and I think I have sufficient deference to support my findings and decision, as I did 4 tests for each concentration.
I think my results are reliable however, with improved equipment we could have made this experiment more precise, as some gas may have leaked out of the tubing.
If I was to do this experiment again I would use equipment that would be more accurate at measuring the volume of gas produced. However I would probably still use concentration as my variable, because is easy to measure out concentrations and they gave be quite accurate results. To extend this activity I could do tests with more concentrations to backup my findings even more. I could also get other people to do the experiment as I may do the experiment in a different way to others, so this would give me a better overall average.